1. Field of the Invention
The present invention relates to radio communication systems, and, more particularly, to an apparatus and method for increasing the data transmission rates within an analog cellular communication device.
2. Description of the Related Art
Radio communication systems have become an important part of the overall communications network in the private, business, and government sectors. Radio communications systems offer a number of significant advantages over wireline or other communications systems. Most significantly, radio communication technology provides substantially greater flexibility than wireline systems, which typically provide communication access at a single geographic location. However, present radio communications systems also have a number of significant limitations as well. Perhaps the most serious limitation to present radio communications systems is the limited amount of data which is able to be transmitted via radio communication.
Many radio frequency bands are presently used for wireless communication systems. For example, the cellular band, police, fire and military bands, business bands, etc. Although the present invention will be described with reference to the analog cellular communication band, it will be understood that the teachings of the present invention apply to all radio frequency transmission.
The limitations observed in the data transmission rate for radio communications systems is especially prevalent in analog cellular communication systems. While modems might appear to connect at a 9600 bit per second modulation rate, actual throughput has typically been achieved at only 200-400 characters per second (as opposed to 960 characters per second as a 9600 bps rate would suggest). The lower throughput exhibited in conventional systems is due to link layer errors and packet retransmission. For an example of the previously attainable bps modulation rates, see an article entitled "New Protocol For Cellular Transfers" published in Communications Weekly, dated Jul. 5, 1993.
Ideally, in order to make radio communication systems a viable alternative to wireline systems in the field of data communication, the data throughput rate over the radio frequency communication system should be at or near the data throughput rate obtainable in wireline systems. Presently, however, the data throughput rate for cellular and other radio frequency communication systems is significantly lower than the data throughput rates obtainable in wireline communication systems. Furthermore, although significant advances have been made to increase the maximum data transmission rate in analog cellular communication systems, the present maximum data transmission rate is well below that needed for certain data communication applications. Specifically, many graphic related data transmission applications require a bit rate in excess of 9,600 bits per second to be viable for commercial use or other important applications. For example, one application involving cellular data transmission uses a cellular modem to transmit graphic images to an emergency vehicle (such as a fire engine) so that, for example, the floor plan of a burning building, and other important information, can be accessed by emergency personnel while in transit. If the graphic information is transmitted at a rate that is too low, the information may not reach the emergency personnel in time to be useful. In addition to emergency applications, an increased data transmission rate is important to the implementation of systems wherein large data files are to be transmitted in a reasonable time and at a reasonable cost. For example, see an article entitled "Better Mobile Network Infrastructure Needed" published in COMPUTERWORLD magazine, dated Jun. 28, 1993. Thus, a plurality of applications exist whose circumstances necessitate increased data transmission rates in order for these communications systems to be viable.